Testicular epidermoid cyst
The sonogram of the left testis revealed a heterogeneous,
well-circumscribed intratesticular mass, composed of mixed
hypoechoic and hyperechoic components with discontinuous
curvilinear, somewhat concentric, highly reflective echoes. Small
focal punctate echogenicities were also noted. The mass measured
2.9 * 2.6 * 2.9 cm and was avascular.
Testicular epidermoid cysts are classified as benign germ cell
tumors that comprise approximately 1% to 2% of all resected
testicular masses.1,2 They are found most commonly in
males in their second through fourth decades of life.1,3
A typical presentation is a painless testicular nodule incidentally
discovered during physical examination.1,4
Alternatively, diffuse testicular enlargement is noticed in
approximately 10% of cases.1,5 These presenting symptoms
overlap with those of malignant testicular neoplasms.
At pathological examination, testicular epidermoid cysts are
well-circumscribed solid masses, confined by the tunica albuginea.
The lesions are encapsulated by a fibrous wall containing an inner
layer of squamous epithelium.6 This fibrous wall often
becomes calcified, and sometimes, even ossified.4 Within
the center of the cyst is thick, pasty squamous epithelium and
The classification of testicular epidermoid cysts within other
categories of testicular lesions is controversial. Many believe a
testicular epidermoid cyst to be the end result of a teratoma that
has undergone monodermal or monomorphic differentiation, as it
contains only the epidermal portion of ectoderm.1,4,5
However, testicular epidermoid cysts exhibit no malignant
potential, as testicular intraepithelial neoplasia, a histologic
precursor for germ cell tumors, is absent. This has called into
question the germ cell origin of epidermoid cysts.7
Currently, the World Health Organization classifies testicular
epidermoid cysts as "tumor-like lesions."7
Long-term follow-up has been possible in several series of
patients who have undergone testis-sparing surgery. After resection
of testicular epidermoid cysts, patients have remained disease-free
for up to 23 years post-surgery with neither local recurrence nor
distant metastases.1,4,7,8 While definitive diagnosis
requires histologic examination, suggestive preoperative imaging
findings of an epidermoid cyst can prepare the surgeon and the
patient for a testis-sparing enucleation of the mass. This more
conservative approach, with intraoperative frozen-section
histologic analysis, can prevent unnecessary radical
The key to utilizing this approach, therefore, lies in the
preoperative imaging findings. The testicular epidermoid cyst may
have a variable sonographic appearance, but some features
suggestive of the histologic diagnosis have been
identified.9 Testicular epidermoid cysts are generally
well defined sonographically, with a hyperechoic rim cor-responding
to the dense fibrous capsule. If any calcification of the capsule
has occurred, it will exhibit the typical hyperechogenicity with
acoustic shadowing. Concentric rings of alternating hypo- and
hyperechogenicity within the cyst (the so-called "onion-ring"
appearance) correspond to the histologic finding of alternating
layers of compacted keratin and loosely arranged desquamated
squamous cells.7 Within the lesion, an echogenic focus
may have formed as the innermost keratinized debris became
compacted centrally, producing a "target" or "bull's-eye"
appearance.10 These characteristic sonographic features
should alert the radiologist to the benign nature of these masses.
In this case, sonographic findings were not classic and the mass
was thought to be a malignant germ cell tumor. Although any solid
intratesticular mass should be considered to be a neoplasm until
proven otherwise, the radiologist should seek a target sign or
curvilinear calcification in a concentric configuration, even if
the rings are incomplete. If found, the surgeon should be alerted
to the possibility of an epidermoid cyst, which may permit an
attempt at testis sparing enucleation rather than a radical
1. Shah KH, Maxted WC, Chun B: Epidermoid cysts
of the testis: A report of three cases and an analysis of 141 cases
from the world literature. Cancer 47:577-582, 1981.
2. Price AB Jr: Epidermoid cyst of the testis:
A clinical and pathological analysis of 69 cases from the
testicular tumor registry. J Urol 102:708-713, 1969.
3. Caravelli JF, Peters BE: Sonography of
bilateral testicular epidermoid cysts. J Ultrasound Med 3:273-274,
4. Malek RS, Rosen JS, Farrow GM: Epidermoid
cyst of the testis: A critical analysis. Br J Urol 58:55-59,
5. Buckspan MB, Skeldon SC, Klotz PG, et al:
Epidermoid cysts of the testicle. J Urol 134:960-961, 1985.
6. Dambro TJ, Stewart RR, Carroll BA: The
scrotum. In: Rumack CM, Wilson SR, Charbonneau JW (eds): Diagnostic
Ultrasound. pp. 791-821. St. Louis, Mosby, 1998.
7. Dieckmann KP, Loy V: Epidermoid cyst of the
testis: A review of the clinical and histogenetic considerations.
Br J Urol 73:436-441, 1994.
8. Ross JH, Kay R, Elder J: Testis sparing
surgery for pediatric epidermoid cysts of the testis. J Urol
9. Langer JE, Ramchandani P, Siegelman ES, Banner
MP: Epidermoid cysts of the testicle: Sonographic and MR
imaging features. AJR Am J Roentgenol 173:1295-1299, 1999.
10. Brenner J, Cumming WA, Ros PR: Testicular
epidermoid cyst: Sonographic and MR findings. AJR Am J Roentgenol
152:1344, 1989. Letter.